Author: Amber Patterson

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Short-term bio-electrochemical pretreatment of dairy manure for efficient sulfide remediation prior to anaerobic digestion

Purpose

According to the latest estimation of Food and Agriculture Organization of the United Nations, the global dairy cattle stocks reached over 265 million in 2019. The massive stocks of dairy cows excrete an enormous amount of manure, which is a huge burden to the environment if unproperly disposed of, thus necessitating proper manure treatment. As such, anaerobic digestion (AD) has been widely adopted as a practice to manage dairy cattle manure. Within the United States, digesters at dairy farms started to be widely constructed after 2000, and the number of these on-farm digesters in operation or under construction has increased to over 400 in 2024. During the AD treatment of dairy manure, the sulfate-reducing microorganisms are active under anaerobic conditions, therefore high levels of hydrogen sulfide (H₂S) are common in biogas because of the degradation and conversion of sulfur-bearing organics in feeding materials and sulfate-bearing minerals in bedding materials within the manure stream. As an extremely toxic gas with an acute rotten egg odor, H₂S is one of the leading causes of workplace gas inhalation deaths in the US according to the Bureau of Labor Statistics. In addition to the health risks, high H₂S levels can be also very corrosive to the equipment and infrastructure: long-term exposure to concentration of H₂S greater than 1 ppm reduces the lifespan of structural materials, equipment, and electronic devices inside the facilities. Therefore, it is an urgent task to mitigate the H₂S emissions in manure management.

Conventional H₂S removal technologies typically include two categories, namely ex-situ and in-situ. The ex-situ biogas cleaning technologies (e.g., biofilters, aqueous solutions, iron sponge, etc.) require a separate unit to house the facilities and are chemical- and energy-intensive. In-situ H₂S mitigation methods usually require less energy and chemical input as well as an easier operation. In our previous study which employed bio-electrochemical (BEC) treatment concurrently with AD of dairy manure, a H₂S removal efficiency of over 95% was successfully achieved, thus offering a very promising in-situ H₂S remediation method. Nonetheless, it was operated in a continuous mode with electrodes inserted into the digester, which would require significant modification of existing AD systems when scaled up. Therefore, developing new strategies that can advance the application of BEC H₂S remediation within the conventional AD system is critical.

What Did We Do?

Most large sized farms collect liquid manure and slurry in a reception pit (or transition pit) before manure is pumped to the anaerobic digesters. This pit is usually open to the air, thereby offering a great opportunity to integrate the BEC treatment in dairy manure management. In the present lab-scale study, a BEC unit was applied to pretreat the dairy manure collected from the transition pit. On the basis of our previous study, a combination of low carbon steel (LCS) anode and stainless-steel cathode was selected as the electrode pair. At the applied voltages of 1.0-2.5 V, the dairy manure was pretreated for 24 hours prior to AD tests. After the BEC pretreatment, the peak H₂S concentration in the biogas was reduced from approximately 6,000 ppm (in the control without BEC pretreatment) to below 420 ppm in the groups at the applied voltages over 1.5 V. The total H₂S removal efficiencies reached 48.9%, 89.1%, 98.5%, and 100% at 1.0 V, 1.5 V, 2.0 V, and 2.5 V, respectively, equivalent to the sulfide removal of 18.6, 33.4, 36.9, and 37.4 mg S²⁻/g wet dairy manure. Nonetheless, higher voltages did not trigger higher biogas production. Besides, due to the anodic oxidation that released some CO₂ and the precipitation of carbonate (e.g., CaCO₃) in BEC pretreatment, the CH₄ contents in the yielded biogas from BEC groups (64.5-65.6%) were all slightly higher than that from the control (63.4%). Moreover, it was noteworthy that the technical digestion time (T80) (i.e., the time needed to produce 80% of the maximal digester gas production) was shortened to 28.0-29.3 d in the BEC groups at 1.5-2.5 V as compared to 32.8 d in the control. This suggests that the BEC pretreatment can remarkably accelerate biogas production in addition to the H₂S remediation. Groups using non-sacrificial electrodes (e.g., graphite sheets and rods) were also established for the 24-h BEC pretreatment of dairy manure. However, in subsequent AD tests, a large quantity of gaseous H₂S was still emitted. The comparison between the groups with and without sacrificial LCS anodes indicates that the formation of insoluble ferrous sulfide (FeS) was the main route of sulfide removal, whereas the contribution of anodic sulfide oxidation to sulfate and elemental sulfur was relatively limited.

With all the selections and optimizations above, a pilot-scale electrochemical unit was accordingly designed and then installed and operated in the dairy manure pit in a local dairy farm in Minnesota for over two months (as shown in Fig. 1), and its effects in in-situ H₂S remediation in a real application scenario were documented. This pilot-scale BEC system reduced the headspace H₂S level from 1,808 ppb to 390 ppb with a removal efficiency of 78.4%.

Fig. 1 Pilot-scale BEC system installation and operation in dairy manure transition pit
Fig. 1 Pilot-scale BEC system installation and operation in dairy manure transition pit

What Have We Learned?

This lab-scale success as well as the pilot-scale implementation supports BEC as a promising method for integration into existing on-farm AD systems treating dairy manure. With its incorporation of a BEC unit into the open-air manure transition pit, the operation could be simplified to a large extent without the considerable modification of existing AD systems, whilst the H₂S remediation and the improvement in biogas production (in both CH₄ content and technical digestion time) could be simultaneously achieved at an optimum applied voltage. In summary, this proposed BEC system can successfully reduce the H₂S and improve the safety of a dairy farm during manure storage and treatment.

Future Plans

In our future research, we will further assess the sulfur distribution and microbial community changes after both lab-scale and pilot-scale BEC treatment and also optimize the BEC strategy to reduce anode consumption. Besides, a techno-economic analysis and a life cycle assessment are now under evaluation, based on the data obtained through both the lab-scale tests and the pilot-scale demonstration, to further explore the feasibility and applicability of a full-scale BEC system in a real dairy farm scenario.

Authors

Presenting author

Lingkan Ding, Researcher Pro 5, University of Minnesota

Corresponding author

Bo Hu, Professor, University of Minnesota, bhu@umn.edu

Acknowledgements

The authors greatly appreciate funding support from USDA NRCS Conservation Innovation Grant (NR213A750013G029) and the assistance of Dennis Haubenschild for on-site work on the farm.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date. 

 

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Animal Waste Training for NC Food Animal Producers

Purpose

North Carolina Cooperative Extension takes a lead role in providing education and training opportunities for animal waste management.  Extension provides certification classes for operators on permitted animal farms and for technical specialists who advise and assist those operators.  Extension has been the lead agency to train producers and technical specialists via continuing education classes, field days, and tours. All permitted animal waste facilities must have at least one licensed operator in charge (OIC) on the farm to ensure all rules and regulations are followed.  Training for these groups is mainly done at the county level by Extension Agents assisted by specialists. This poster provides an overview of the activities of the NC Extension team towards Animal Waste Management Training.

What Did We Do?

Extension educates food animal producers through three main activities:

    • Initial OIC Class: Would-be operators attend a mandatory 10-hour class after which they sit for a 50-question exam administered by state agencies. Those passing the exam are designated as certified OICs.  These classes are offered annually by county extension agents in key production counties. There are two types of OIC certification: type A certification for swine and liquid poultry systems and type B for dairy, horse, beef and other high fiber systems.
    • Continuing education classes for OICs: All OIC’s must receive 6 hours of continuing education credit every 3 years.  In 2024, there were 1,924 type A operators and 216 type B operators across the state. Agents and specialists provide the majority of continuing education classes for OICs either in-person or through statewide online classes.  Topics include waste utilization, new technologies, safety, weather readiness, planning for extreme events and disease outbreaks, ventilation, sludge management, and many more.
    • Continuing education classes for Technical Specialists: Agents and specialists also provide the majority of continuing education classes for technical specialists as part of their requirement to receive 6 hours of credit every 3 years.  There is typically a yearly field day or tour participants can attend to meet this requirement.  Around 30 participants usually attend.

What Have We Learned?

There are over 2,100 operators in NC who need continuing education training every 3 years. The requirement for OICs has been around since 1996.  Extension agents and specialists need to work together to provide the highest caliber programs to keep producers engaged, up-to-date, and excited to learn about changes and challenges in NC.  The statewide online option allows agents with less experience in animal waste topics to offer quality programs from top experts in the state and to learn about emerging practices, technologies, and recommendations.  Google form surveys are used to measure knowledge gained, adoption of new practices, and recommendations on future topics.  The agent-specialist group uses the recommendations from surveys to choose future topics and speakers.  Surveys show that OICs are interested in these topics: irrigation calibration, crop and pasture/hayfield management including pest management, lagoon clean out and sludge management, new technologies including digesters and alternative waste facility options.  Technical specialists are interested in lagoon closures, sludge management and utilization, new technology – digester, land applying to pine trees and other alternative crops.

Future Plans

NC State Extension has an animal waste workgroup which is made up of specialists and agents.  This work group is allocated money each year to purchase supplies and materials that will help in programming.  This group helps determine the educational needs of agents, farmers, and technical specialists in the state and works to make sure those needs are met.  The group plans to continue to improve the educational courses offered and determine the best methods of communication to maximize engagement and learning.  The group uses surveys to guide topic and speaker selection.  Future plans include filming more videos to use in educational programs.

Authors

Presenting & Corresponding author

Becky Spearman, County Extension Director and Livestock Extension Agent North Carolina Cooperative Extension – Bladen County, becky_spearman@ncsu.edu

Additional authors

Dr. Mahmoud Sharara, Extension Specialist, North Carolina State University

Dr. Steph Kulesza, Extension Specialist, North Carolina State University

Additional Information

NCSU Animal Waste Portal

Department of Environmental Quality Animal OIC website

Animal Waste Manual Type A (2021)

Animal Waste Manual  Type B (2017)

Q&A: Installing Anaerobic Digesters on NC Swine Farms YouTube Video
Innovation in Swine Manure Management

Acknowledgements

The following Livestock Extension Agents: Amanda Hatcher (Duplin County), Max Knowles (Sampson County), Nancy Keith (Iredell County), Stefani Sykes (Wayne County), and Kaelyn Mohrfield (Lenoir/Greene Counties)

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date.

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Turning Dairy Manure Into P-rich Hydrochar, a Conceptual Design of Continuous-Flow HTC System

Purpose

Dairy manure was once considered a waste, but it can be transformed into a valuable resource. As demand for sustainable waste management grows, innovative ways for converting dairy manure are being actively researched to enhance both dairy productivity and environmental sustainability. One such method, hydrothermal carbonization (HTC), has recently garnered significant attention due to its ability to convert wet biomass into value-added products. HTC involves treating wet biomass, such as dairy manure with high water content, at moderate temperatures (180℃-250℃) and pressure. The outcome of HTC is hydrochar, a solid product with high carbon and nutrient content.

Hydrochar has strong potential as a means of soil amendment, carbon sequestration and/or biofuel. Our lab scale experiments showed that hydrochar retains more than 90% phosphorus (P) from dairy manure.  For hydrochar production to become a viable technology for dairy farms, a continuous system is essential. Such a system would offer numerous benefits, including increased production, enhanced efficiency, and greater potential for commercialization. The purpose of this study is to design a pre-commercial conceptual process for the continuous production of hydrochar from dairy manure.

What Did We Do?

Manure management consists of collecting manure from the floor to utilize it in the best possible way. Most dairy farms treat manure through anaerobic digestion to produce energy, separate the solids for use as a bedding material, and/or apply directly to field applications. To explore alternative ways of handling the large quantities of manure in a quick chemical method and recycling nutrients back to the cropland, dairy manure is processed into P-rich hydrochar via an HTC process. Based on the results of our laboratory experiments, a conceptual process was developed, which is capable of treating dairy manure from a mid-size farm with 1,000 lactating cows and equates to 38,000 tons of manure per year with 8-10% solids. The process design includes engineering designing details of manure preparation and handling, feeding and discharge mechanisms, main equipment (such as HTC reactor and heat exchangers), heating and temperature controls, and schemes for post-HTC process wastewater (post-water) handling. Figure 1 is the schematic of the conceptual process with major process equipment, where the thick, black lines indicate the flow of dairy manure slurry containing solids, while the thin, blue lines represent the flow of post-processed water.

Firstly, dairy manure collected from the dairy barns (approx. 10% solids) is stored in a storage tank (T-101) before being pumped into the feeding tank (T-102), where it is heated to 167°F (75°C) by the recycled post-water from preheater I (E-201) through internal heating coils. The feeding tank is equipped with a marine-style impeller for agitation to maintain solid suspension. Two preheaters (E-201 and E-202) are used to further heat the slurry to the required HTC temperature before entering the reactor (R-301). Preheater I is a shell-and-tube heat exchanger to heat the slurry up to 320°F (160°C) by heat recovery using the hot post-water from post-water tank (T-304).  Preheater II is a tubular electric heater and is to finish the last stage of heating to 437°F (225°C). A continuously stirred tank reactor (CSTR) with agitation is the main equipment to thermochemically process dairy manure into hydrochar. After a 30-minute retention time in the reactor, the resulting product mixture is collected in the receiving tank/separator (T-302). Then the hot post processed-water is separated from the solid (the wet hydrochar cake) and collected in a storage tank (T-304) before being used as a heating medium for heat recovery. The wet hydrochar cake coming out of decanter centrifuge (T-303) is dewatered through an air-drying unit (C-305) to a water content of 12% or less, which can be used directly for land applications or packaged and transported to other markets.

Figure 1 Schematic of the conceptual process with major process equipment.
Figure 1 Schematic of the conceptual process with major process equipment.

What Have We Learned?

Continuous hydrochar production holds great potential for recycling phosphorus from dairy manure back into the cropland as a soil amendment and for sequestrating carbon back to the soil. The conceptual process represents a significant step towards practically promoting this alternative manure treatment technology and creating a value-added product for nutrient cycling. This process is capable of producing approximately 5 million pounds (2,300 metric tons) of air-dried hydrochar per year, a yield of about 60% of the solid matter from dairy manure, and with a phosphorus concentration of approx. 1.4 lb/100 lb. Hydrochar is hydrophobic and can be sufficiently dried by ambient air. The air dried hydrochar contains a moisture content of 12% or less (as low as 5% per laboratory results due to hydrochar’s hydrophobic characteristics) and is suitable for long term storage and/or distance transportation. Because the raw, wet dairy manure can be processed directly from the farm without any pretreatment, the HTC process offers a good possibility for a cost-effective waste management alternative while producing valuable hydrochar for phosphorus recycling.

Future Plans

Upon completing this continuous flow process design, we will conduct a techno-economic assessment (TEA) to provide insights into the system’s economic feasibility, cost structure, and profitability. The TEA study will also offer a better perspective on the economic viability, technical challenges, and potential profitability of adopting and investing in the continuous hydrochar production system from dairy manure for waste management and nutrient cycling.

Authors

Presenting author

Imran Hussain Mahdy, Graduate Student (Ph.D.), University of Idaho

Corresponding author

Brian He, Professor, University of Idaho, bhe@uidaho.edu

Acknowledgements

USDA AFRI, UADA NIFA and Idaho Agricultural Experiment Station are acknowledged for their financial support through Sustainable Agricultural Systems (SAS) program (Grant 2020-69012-31871), and hatch project of IDA0-1716 (Accession number1012741).

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date. 

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Modeling of Electrochemical Ammonia Removal from Anaerobically Digested Dairy Wastewater

Purpose

Ammonia (NH3) found in anaerobically digested dairy wastewater (ADDW) could pose a serious threat to the environment. Various methods, including ion exchange and reverse osmosis, have been employed to remove ammonia from ADDW. While these techniques can be effective, they have significant drawbacks, particularly the generation of highly concentrated wastewater as a byproduct. This concentrated effluent poses a considerable challenge for safe disposal, potentially leading to secondary environmental impacts if not managed appropriately. As a result, while these methods address ammonia removal, they often shift the burden to another critical area, necessitating the development of more sustainable and holistic wastewater treatment solutions. In recent years, an electrochemical approach has garnered significant attention as an innovative and efficient alternative for wastewater treatment. This method is gaining growing recognition for its effectiveness in degrading a broad spectrum of pollutants, including ammonia, with minimal chemical additives. Its versatility, coupled with the potential for on-site application and reduced secondary waste production, makes electrochemical treatment a compelling solution for addressing the challenges posed by traditional wastewater treatment technologies. Different active radicals (•OH, OH–) generated during electrochemical process are used to oxidize NH3 to nitrogen gas (N2) and increase the selectivity of N2 (Eq. 1-4). The selectivity of N₂ in ammonia decomposition measures how much of the nitrogen from NH₃ is converted into N₂ gas instead of forming other nitrogen-containing byproducts.

(1) 2NH3 + 6OH– → N2 + 6H2O + 6e–      

(2) NH3 + •OH → •NH2 +H2O

(3) NH2 + •NH2 → N2H4

(4) N2H4  →  N2 + 2H2

Not many studies have looked into how ammonia breaks down during electrochemical treatment or how to predict this process. One common problem is that ammonia undergoes oxidation beyond the desired or controlled extent, leading to the formation of undesirable products like nitrate (NO3–), nitrite (NO2–) etc.   Achieving high ammonia removal efficiency and selective conversion to non-reactive N₂ gas is critical for optimizing electrochemical treatment. The purpose of this research was to investigate the viability and kinetics of electrochemical treatment for improving dairy wastewater quality through ammonia removal at different current densities.

What Did We Do?

Anaerobically digested dairy wastewater was sourced from a commercial dairy facility in southern Idaho and was stored at 39.2°F prior to the experiment. The concentrations of ammonia, nitrate, and nitrite in the collected wastewater were measured using a Hach DR 5000 spectrophotometer.

In the electrochemical reactor, a niobium-based boron-doped diamond (BDD/Nb) electrode was used as the anode, while a graphite plate served as the cathode (Fig. 1). Both electrodes had a working surface area of 3.10 in2 (20 cm²), with the interelectrode gap kept constant at 0.39 inch (1 cm).

Figure 1. Experimental set-up.
Figure 1. Experimental set-up.

Different levels of electric current (20, 30, 40, and 50 mA/cm2) were applied to study their effect on how ammonia was efficiently removed. The breakdown process of ammonia was analyzed using a mathematical model called pseudo-first-order kinetics. Additionally, changes in ammonia, nitrate, and nitrite levels and production of N2 gas were recorded over a 120-minute treatment period. The connection between the reaction speed and the applied current was also examined.

What Have We Learned?

Figure 2 illustrates the effect of applied current density on the removal of ammonia during the electrochemical treatment of ADDW. The removal of ammonia increased substantially with higher applied current densities (from 20 to 50 mA/cm2), with removal efficiency of 80.12% to 98.26% during a 120-minute treatment time. The applied current density is a critical operating factor that influences the electrochemical reaction by regulating the generation of active radicals on the electrode surface. This trend can be attributed to the fact that higher current densities enhance the formation of active radicals, which in turn accelerates the ammonia oxidation rate.

Figure 3 shows that ammonia removal at various current densities followed the pseudo-first order kinetic model. The relationship between the reaction rate constant (min-1) and applied current density (mA/cm2) demonstrated an exponential function with a high correlation coefficient value (R2= 0.98) (Fig. 4). This supports the accuracy of the pseudo-first order kinetic model in describing ammonia removal from ADDW. From the concentration profile, it is clear that a substantial amount of nitrogen was released from the system into the gas phase, primarily as N2 gas. This nitrogen loss from the system was estimated based on the total nitrogen mass balance. Ultimately, the selectivity of nitrogen reached to 90%. It was noted that the concentration of NH3 declined over time during the electrochemical treatment, with only a small amount of NO3− and NO2− being produced. The final concentration of NO3− and NO2− were 140 mg/L and 0.87 mg/L respectively. It has been documented that NO2⁻ can undergo reactions with NH3 to form N2 or be oxidized by oxygen gas (O2) to produce NO3⁻. This likely explains why the final concentration of NO2⁻ was lower compared to that of NO3⁻.  All of these findings clearly demonstrate that the electrochemical treatment can effectively remove ammonia from ADDW and achieve high nitrogen selectivity.

Figure 2. Effects of applied current densities on ammonia removal efficiency.
Figure 2. Effects of applied current densities on ammonia removal efficiency.
Figure 3. Pseudo-first order kinetic model for ammonia removal at different current densities.
Figure 3. Pseudo-first order kinetic model for ammonia removal at different current densities.
Figure 4. Relation between reaction rate constant and applied current density.
Figure 4. Relation between reaction rate constant and applied current density.

 Future Plans

In the future, we will work on nitrogen and phosphorus recovery simultaneously from dairy liquid manure by applying electrochemical treatment approach.

Authors

Presenting author

Ashish Kumar Das, Ph.D. Student, Environmental Science Program, College of Natural Resources, University of Idaho

Corresponding author

Dr. Lide Chen, Professor, Department of Soil and Water Systems, Twin Falls Research and Extension Center, University of Idaho, lchen@uidaho.edu

Acknowledgements

This research was funded by the USDA Sustainable Agricultural Systems Initiative through the Idaho Sustainable Agriculture Initiative for Dairy (ISAID) grant (Award No. 2020-69012-31871).

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date. 

 

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Pilot-scale Composting System to Measure Air Emissions from Dairy Manure and other Byproducts

Purpose

The overall objectives of this research are to investigate the design, implementation, and evaluation of a pilot-scale composting system for dairy manure. This composting system was developed because of the significant quantities of dairy manure produced in Idaho and the need to improve dairy compost quality while reducing air emissions during the composting process. This composting system provides the ability to simulate on-farm composting in Idaho while measuring and regulating key composting parameters, gas emissions, and implementing changes during operation.

What Did We Do?

This pilot-scale composting system was developed by adapting a home composter to simulate a mechanically turned windrow system. The composters were modified to include aeration control, air monitoring equipment (Gasmet), and measure key composting parameters throughout the process. Ten compost reactors were built, which allowed for several combinations of treatments and multiple replications. Each reactor is connected to a plenum with the capacity to interconnect several reactors or isolate each one and regulate airflows and chamber pressure. During the initial trial, two replications of each amendment: control, biochar, pumice, wood chips, and zeolites were evaluated. A follow-up trial will repeat the two replications per treatment, for a total of four replications. Modifications of the composting system during the trial addressed challenges with moisture control, odor, temperature regulation, air velocity, and compost balling.

Figures 1 and 2 define the blocking pattern and layout of the composting system for all ten compost reactors. The blocking pattern was generated for two primary reasons: Create replications for each treatment and compensate for a temperature differential between both ends of the research space caused by the cooling method in the greenhouse.

Figure 1. Diagram of air plenum that hangs above the compost reactors. Source: Authors

Figure 2. Diagram of gasmet tubing color coded with three separate lengths of PTFE tubing to each reactor. Source: Authors

What Have We Learned?

We learned that the pilot-scale composting system can effectively simulate different types of on-farm composting methods, demonstrating its adaptability for research. During the composting trial, the aeration was regulated to simulate forced and natural airflow composting systems. The ability to continuously measure the headspace size confirmed a significant decrease in composting volume, as expected in a full sized composting system. The temperature monitoring showed we were able to reach thermophilic composting for the first two weeks of the trial and showed temperature increases at each turning event. These findings indicate that this system can be a valuable tool for developing more efficient on-farm dairy manure management practices at the pilot-scale.

Future Plans

The design and implementation of this composting system have only completed one trial run. The immediate next step is to complete another round of the compost trial. Each resulting compost mix with the corresponding amendment will be tested in a crop-testing greenhouse trial. The amount of compost, or any other products, handled by these reactors allows for further tests in the lab, at the pilot scale, or in a greenhouse.

In the short term and beyond the dairy manure trials, the reactor system will be tested for other processes, including different composting techniques and amendments. Other processes to be tested include soil amendments and their impact on air emissions, anaerobic digestion without mixing, emissions from diverse waste streams and amendment combinations, among others.

Authors

Presenting author

Anthony Scott Simerlink, Assistant Professor, Extension Educator – Power County, University of Idaho

Corresponding author

Mario E. de Haro-Martí, Professor, Extension Educator – Gooding County, University of Idaho, mdeharo@uidaho.edu

Acknowledgements

Funding for this project was provided by a USDA-NIFA Sustainable Agriculture Systems (SAS) grant #2020-69012-31871.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date. 

 

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Community Engagement to Mitigate Transmission of Infectious Diseases and Antibiotic Resistance from Backyard Poultry

Purpose

Backyard poultry production is growing globally with 85 million backyard chickens estimated in the U.S. (Mace & Knight, 2024). Whether kept as pets or to provide a local and sustainable food source, flocks can harbor pathogens and antibiotic-resistant bacteria that can be transmitted to humans via the environment, pests, food products, and direct contact. Poultry waste can contaminate soil and water sources, posing risks to nearby humans and other animals. Flocks can attract pests that may carry diseases and disrupt local ecosystems. This project, which will launch in the summer of 2025, aims to improve understanding among backyard poultry farmers of potential health, environmental, community, and food safety risks associated with their systems and motivate the adoption and promotion of behaviors critical to public health and sustainability of local food systems using a peer-to-peer outreach approach.

This project will evaluate an approach to motivating behavioral changes among a cohort of backyard poultry farmers that is predicated on evaluating current flock management practices among participants, improving understanding of health risks associated with current practices, and motivating implementation of recommended practices to mitigate health risks. Beneficiaries of project outcomes include members of households in which chickens are maintained, local community members, consumers of local poultry products, and the broader population that shares environmental resources with these sites and are impacted by human health threats. Our project will uniquely address multiple facets of backyard poultry production that contribute to human health, environmental sustainability, food safety, and community well-being through engagement with existing poultry owners to improve knowledge, promote the adoption of best practices, and facilitate communication networks. Assessments of current production practices among participating local backyard poultry farmers will inform educational needs related to managing these systems for environmental and public health benefits. Facilitated engagement among participants during educational events will promote shared goals, motivate practice adoption, and build confidence among participants in their role as citizen scientists capable of promoting a broader community understanding of the topics addressed.

What Did We Do?

The overall goal of this project is to mitigate potential disease transmission risks to humans from small poultry flocks by delivering data-informed educational programming and assessing subsequent behavioral changes among audience members. After a thorough investigation using previous studies conducted on the impact of community engagement in health education, we have designed our research to identify, deliver, and assess an effective methodology to achieve the following objectives.

Objective 1: Evaluate the knowledge, perceptions, and practices among backyard poultry farmers that may contribute to their risks for acquiring AMR genes/infections from their birds using a Reasoned Action Approach.

Figure 1: Graphical representation of the Reasoned Action Approach, a psychological model to explain and predict behavior
Figure 1: Graphical representation of the Reasoned Action Approach, a psychological model to explain and predict behavior

Objective 2: Quantify the contribution of backyard poultry manure and bird management practices to the presence and concentration of pathogenic organisms and resistance genes in the environment via sampling and analysis of manure, soils, runoff, and flying insects.

Objective 3: Develop, deliver, and assess impacts of educational programming designed to motivate the adoption of new integrated antimicrobial management approaches in backyard poultry farming to reduce the potential spread of AMR.

Thirty backyard poultry farmers from up to three counties in Nebraska will be recruited through community groups, personal connections, and university extension contacts. Participants will be surveyed and observed to understand their current knowledge, perceptions, and management practices, and identify knowledge gaps related to bird health, biosecurity, and disease transmission risks. The Reasoned Action Approach, a social cognitive model for behavioral analysis will be used to categorize the data, predicting and explaining their behavior towards healthy farming practices. The mixed-methods study will use standard statistical methods and qualitative data for a richer interpretation.

Sampling of environmental matrices and potential insect transmission vectors will be conducted and used to complete a risk factor assessment to understand disease demography.

Through face-to-face and digital sessions, engagement and education sessions will be designed to address knowledge gaps in poultry handling, waste management, personal hygiene, water quality, food safety, and human health risks. It will promote best practices and encourage participation through rewards, project-based learning, on-farm demonstrations, and regular reflection on personal impact. The recruited farmers will be appointed as trainers for other farmers in their locality to continue to promote the learning outcomes from the training. The training sessions will be assessed through a post-training survey using a knowledge-based questionnaire, and all discussions with farmers will be recorded for future evaluation. This data will help determine improvements for future outreach events on infectious disease control in backyard poultry farms, enhancing the training’s impact.

What Have We Learned?

The number of households engaging in “backyard poultry production” is growing regionally, nationally, and globally. Evidence also suggests that chickens are not strictly confined to the outdoors but are becoming indoor “pets,” creating complex human-chicken relationships responsible for zoonotic disease outbreaks and antibiotic resistance risks (Singh et al., 2018; Tobin et al., 2015). According to a 2010 study, the USDA confirmed almost 50% of the population related to backyard poultry production lacks knowledge about human health risks associated with contact with live birds (USDA, 2011). Studies reflect a critical need for decision-making support to ensure healthy birds, applying biosecurity practices that mitigate animal-to-human disease transmission risks and development of antibiotic-resistant bacteria, promoting environmental sustainability, and providing healthy local food sources to communities. While these systems represent only a small part of the U.S. poultry industry, their positive impact on local food systems is widely recognized, as are their potential contributions to zoonotic disease transmission, antibiotic resistance, and local ecosystem disruptions. Public awareness about poultry-associated health risks and adopting best practices for biosecurity and disease prevention is critical to balancing healthy local food production with community well-being.

Future Plans

This project aims to improve the health, prosperity, and sustainability of backyard poultry farmers by focusing on zoonotic disease transmission, pest management, and natural resource protection. It will provide training, technical assistance, and peer support to improve knowledge and adoption of best practices for producing healthy local food sources. This will reduce health risks, decrease healthcare costs, and support market access and profitability among urban farmers. The community-based approach will foster mutually beneficial relationships among producers, communities, and experts, promoting sustainable production practices that prioritize health, community needs, and the environment.

Authors

Presenting author

Nafisa Lubna, Graduate Student, University of Nebraska-Lincoln

Corresponding author

Amy Schmidt, Professor, University of Nebraska-Lincoln, aschmidt@unl.edu

Additional author

Mark E. Burbach, Environmental Social Scientist, University of Nebraska-Lincoln

Additional Information

Mace, J. L., & Knight, A. (2024). From the backyard to our beds: The spectrum of care, attitudes, relationship types, and welfare in non-commercial chicken care. Animals, 14(2), 288.

Peters, G. J., & Crutzen, R. (2021). The core of behavior change: introducing the Acyclic Behavior Change Diagram to report and analyze interventions.

Singh, S., Chakraborty, D., Altaf, S., Taggar, R. K., Kumar, N., & Kumar, D. (2018). Backyard poultry system: A boon to rural livelihood. International Journal of Fauna and Biological Studies, 5(1), 231-236.

Tobin, M. R., Goldshear, J. L., Price, L. B., Graham, J. P., & Leibler, J. H. (2015). A framework to reduce infectious disease risk from urban poultry in the United States. Public Health Reports, 130(4), 380-391.

USDA. (2011). Reference of the health and management of chicken flocks in urban settings in four U.S. cities, 2010. Fort Collins, CO: USDA.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date. 

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Integrated Best Management Practices to Minimize Nitrate Leaching in Corn

Purpose

In Nebraska, approximately 117 out of nearly 550 groundwater-based community public water systems are required to conduct quarterly sampling due to elevated nitrate-N levels, with ten systems having already implemented costly treatment measures such as reverse osmosis to mitigate this issue. The intensive production of row crops under irrigation in the state are a primary reason for elevated nitrate concentrations in groundwater. However, the environmental impact of nitrate leaching from agricultural fields is not confined to Nebraska; it is a widespread issue across the US Midwest, where intensive crop production is prevalent.

Despite advances in N management stemming from studies comparing nitrogen fate and transport under synthetic versus manure fertilizers, cover crops versus no cover crops, and other practices, research indicates that when manure is applied following research-based best management practices (BMPs), the risk of nitrate leaching is significantly lower compared to when synthetic fertilizers are applied following BMPs. While individual practices such as cover cropping or manure application have been shown to reduce nitrate leaching, their combined effects on both nitrate leaching potential and crop productivity, particularly in corn (Zea mays L.) systems, have not been thoroughly studied. There remains a critical need to comprehensively evaluate implementation of BMPs that can reduce nitrogen losses to groundwater in Nebraska and utilize evidence-based research to motivate the implementation of BMPs.

This study was conducted to evaluate the effects of the integrated use of beef manure, woodchips, and cover crops on corn (Zea mays L.) productivity and nitrate leaching.

What Did We Do?

A two-year study was conducted on drip-irrigated land with a loamy sand soil having 0 to 2% slopes at UNL’s Haskell Agricultural Laboratory research site near Concord, Nebraska from 2022 to 2023. A total of 24 plots were established, each measuring 6.1 m x 30.48 m, and six treatments were randomly assigned to plots in a factorial combination of two fertilizer sources (manure and inorganic fertilizer), two cover crops (rye cover crop and no cover crop), and two carbon amendment treatments (woodchips of mixed species and no woodchips). Each year, all the plots received the same total N rate, equating to 30% of the total N application broadcasted at planting in the form of Agrotain coated urea, which was calculated using University of Nebraska’s N rate algorithm. The manure plots received the remaining N (70% of the total) in the form of beef manure at planting using a manure spreader. The inorganic plots received the remaining N in the form of UAN side-dressed at the V6 corn growth stage. Each year, inorganic fertilizer plots received additional P, S, and Zn at the time of planting to balance the amount of these nutrients supplied by the manure.

Data collected included:

Soil. Deep core soil samples up to 120 cm were collected before planting in the spring and after harvest each fall, divided into four depths of 30 cm increment, composited by depth within each plot, and stored in a cooler before being transported to the lab for analysis.

Crop. Plant growth parameters assessed at V10 (±1) stage included plant height, leaf chlorophyll, and canopy fullness. Grain yield, harvest index, nitrogen harvest index and partial factor productivity were determined at harvest.

Water. Concentration of NO3-N and NH4-N in the pore water below the root zone was measured one to two times each week throughout the growing season with the help of suction cup lysimeters, two of which were installed 6 m apart between the center two rows of each plot at a depth of 1.2 m.

Cover crop failed to establish in 2023 spring due to dry conditions, therefore, cover crop data and its effects are not reported in this paper.

What Have We Learned?

Key results of this study include:

    • Manure significantly reduced nitrate leaching by providing a slower, more synchronized N release compared to inorganic fertilizers.
    • Woodchip mulch initially delayed N availability and biomass N uptake but ultimately helped reduce nitrate leaching by improving soil moisture retention and temperature moderation.
    • Aboveground biomass N uptake was significantly affected by fertilizer source with manure improving biomass N uptake by 11% compared to inorganic fertilizer.
    • Inorganic fertilizers boosted corn yields by 9% compared to manure treatments, but increased the risk of nitrate leaching, highlighting a trade-off between productivity and environmental impact.
    • Integrated management of manure and mulch was deemed crucial for optimizing N use efficiency and minimizing environmental risks in irrigated corn systems.

Future Plans

Identifying nutrient and land management practices that support sustainable agricultural practices by safeguarding groundwater quality while maintaining farm productivity are critical to the future of agriculture. Future research is expected to focus on refining the practices used in this study to maximize their benefits, including other practices such as in-season nitrogen management, and assessing outcomes under varying environmental conditions and soil types. Nitrogen availability from manure is heavily influenced by environmental and soil conditions, so multi-year data from this site and others should help determine when in-season nitrogen supplementation with inorganic fertilizer is needed to offset nitrogen deficits caused by slow conversion of organic nitrogen.

Because of the failure of cover crops to thrive in this study, future research to assess multiple practices in combination should include a cover crop versus no cover crop treatment.

Combining crop productivity and nitrogen fate and transport data with measures of soil biological conditions may also help identify trends in biological characteristics that contribute significantly to factors like nitrogen conversion and plant nitrogen uptake.

Authors

Presenting & corresponding author

Amy Millmier Schmidt, Professor and Livestock Bioenvironmental Engineering Specialist, University of Nebraska-Lincoln, aschmidt@unl.edu

Additional authors

Swetabh Patel, Assistant Professor, University of Minnesota; Michael Kurtzhals, Graduate Research Assistant, University of Nebraska-Lincoln; Arshdeep Singh, Graduate Research Assistant, University of Nebraska-Lincoln; Leslie Johnson, Extension Educator, University of Nebraska-Lincoln; Javed Iqbal, Assistant Professor, University of Nebraska-Lincoln

Additional Information

https://scisoc.confex.com/scisoc/2024am/meetingapp.cgi/Paper/156921

Acknowledgements

This research was funded by USDA-NIFA Award No. 2022-68008-36509.

The authors extend their sincere gratitude to Logan Dana, Operations Manager at the UNL Haskell Ag Lab, for his role in supporting this project.

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date.

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Evolution of material mixtures for leachate absorption during on-farm disposal of animal mortalities

Purpose

The safe and biosecure disposal of livestock mortalities is a vital concern for livestock producers and the environment. Traditional on-farm livestock disposal methods include composting and land burial, with burial posing environmental risks if leachate generated during carcass decomposition moves through the soil profile to reach groundwater. A 1995 study on the groundwater quality around six poultry mortality piles found elevated concentrations of ammonia and nitrate in the surrounding wells, demonstrating the risk of water contamination from carcass disposal (1). Moreover, the risk of disease transmission to nearby animal facilities associated with an outbreak and large mortality event, particularly due to a foreign animal disease outbreak, dictates that on-farm mortality disposal be conducted in a way that contains and eliminates pathogenic organisms. In the case of a large mortality event, landfills or rendering facilities may not have capacity to receive mortalities or they might refuse to accept them.

On-farm methods accepted in most states include land burial, composting, and incineration. While burial of mortalities often requires less labor and capital cost than composting or incineration, it comes with unique challenges, namely having sufficient space to bury large quantities of animals, adequate soil structure to contain leachate produced during decomposition, and sufficient depth to groundwater to avoid groundwater contamination. Composting is a valuable method as it can destroy many pathogens because of the heat produced in the process, and the by-product is useful. Some of its downsides include the nuisance odor produced and insects such as flies that often accompany the piles. Incineration, while highly effective at reducing volume of carcasses and disease-causing organisms, relies on access to a portable incinerator and sufficient fuel to operate it (2).

Shallow burial with carbon (SBC) is an emerging method for carcass disposal that combines the more common methods of composting and burial. With this method, a shallow pit is excavated in soil and 24 in of carbon material is placed in the trench prior to placing carcasses. The carcasses are then covered using the excavated soil. A field study comparing performance characteristics of SBC and composting for swine carcass disposal (3) found that SBC maintained thermophilic temperatures that met EPA 503(b) time-temperature standards (4), produced less leachate per unit mass of carcasses, and yielded lower contaminant loads (e.g. E. coli) than compost units, suggesting it may also be a suitable mortality disposal method during a foreign animal disease (FAD) outbreak. Further, SBC is a desirable mortality disposal option because it requires less carbon material than composting and does not require management beyond the establishment of the disposal site.

While the previous field study demonstrated lower leachate production from SBC than composting units, the potential may exist to further limit leachate production by identifying carbon materials with greater capacity to absorb liquid produced during carcass decomposition. The primary purpose of establishing a base of carbon material in SBC or composting disposal units is to absorb leachate released during decomposition, reducing the transport of contaminants to water sources. Therefore, this study explored absorbency of several organic materials for inclusion in SBC or mortality compost piles to reduce leachate losses.

What Did We Do?

Our team identified several alternative organic materials for pile construction including wood chips, silty clay loam soil, corn stover, recycled paper pulp (SpillTech(R) Loose Absorbent), and cellulose fiber (Pro Guard Cellulose Fiber). These were tested alone and in combination with 1% by mass (of base material) of sodium and potassium polyacrylate crystals, and 2-mm water gel beads (ZTML MS brand). Hydrogels (HG), sodium polyacrylate (SP), and potassium polyacrylate (PP) were demonstrated in previous studies to retain water in experimental greenhouses (5).

Five replicates of each treatment were enclosed in 4×6 inch cotton mesh bags (TamBee Disposable Tea Filter Bags, Amazon.com) and weighed prior to being submerged in deionized (DI) water at pH 7 for two hours (Figure 1). Bags were removed from the water and allowed to drain for 5 minutes before being weighed again. The bags were resubmerged for an additional 22 hours after which they were removed, allowed to drain for 5 minutes, and weighed again.

Figure 1. Methodology to evaluate absorptivity of treatments
Figure 1. Methodology to evaluate absorptivity of treatments

Five replicates of each combination of base material and absorbent additive were also evaluated using DI water adjusted to pH 3, 5, 7, 8, 10 and using 0.01M NaCl to evaluate the effect of pH on absorbency.

The swelling ratio (SR) of each treatment was calculated using the following formula:

SR = Ww – Wd

where Ww is the wet weight and Wd is the dry weight.

The expected water holding capacity (C) was calculated for each combination.

C = SR ⋅ D

Where C is measured in gallons of water per lb of treatment material and D is the density of base material.

The average of the SR value for the five replications of each combination was further used to determine economic feasibility for retaining leachate from a large-scale mortality compost or burial pile. This was done by first determining the average amount of leachate produced from the mortality piles during the preceding year-long field study in eastern Nebraska (6,030 gallons). This was considered the target volume of material held by an alternative material or combination of materials in the economic assessment.

The volume of leachate was converted to mass, and the swelling ratio average values were used to calculate the mass of base material needed to hold the target quantity of water. These values were then used to calculate the total cost (based on pricing from various sellers) to build a pile of each of these materials that would hold the target volume of leachate. Table 1 shows the price per pound of each material tested; the price of the wood chips, corn stover, and soil were estimated based on these sources, though true price will vary based on region and supplier.

Table 1. Costs of materials evaluated

Material $/lb Source
Wood Chips   0.05 Evans Landscaping
Corn Stover   0.02 MSU Extension
Soil      0.004 Dirt Connections
Recycled Paper   1.84 Grainger
Cellulose Fiber   7.00 Pro Guard
Hydrogel 15.09 ZTML MS
Sodium Polyacrylate   3.71 Sandbaggy
Potassium Polyacrylate 11.38 A.M. Leonard

What Have We Learned?

Results from an analysis of variance (ANOVA) of the SR data showed that SR was not significantly impacted by the soaking time or by pH of the soaking solution. The results also showed that only the addition of 1% SP had a significant effect among the three superabsorbent additives when compared to no additive in the same base material. This effect was relatively equal between all base materials. The other super absorbents (1% HG and 1% PP) did not have a significant effect due to the high variability in the results. The most meaningful differences in absorptive capacity were attributed to base material (Figure 2). On average, the swelling ratio of cellulose fiber (no additives, 24-hour soak, pH 7) is 0.577 gallons water/lb base material. For corn stover, this value is only slightly lower, at 0.447 gallons water/lb base material. Wood chips, the material used in compost piles in the preceding study, had much worse results at only 0.188 gallons water/lb base material.

Figure 2. Mean swelling ratios for organic base materials tested (without additives) after 24-hours soaking in water, pH 7. Letters denote significant differences in water holding capacity, error bars show standard error.
Figure 2. Mean swelling ratios for organic base materials tested (without additives) after 24-hours soaking in water, pH 7. Letters denote significant differences in water holding capacity, error bars show standard error.

The results of the economic analysis are included in Table 2. The corn stover (without super absorbents) emerged as the most cost-effective material, with an estimated $258 total cost of material required to absorb the average amount of leachate observed in a previous yearlong field study that evaluated leachate volume produced from six disposal piles, each containing 20 pigs with a mean weight of 5,826 lb (±90.8 lb). The next most economical option was soil alone ($392) and then corn stover with sodium polyacrylate added ($782).

Table 2. Material cost to retain a leachate volume of 6,030 gallons

Material Mass Required of Base Material (lb) Cost
Woodchips 36,425 $  1,655
Woodchips + SP 36,126 $  2,993
Corn Stover 14,202 $      258
Corn Stover + SP 14,060 $      782
Cellulose Fiber 10,442 $73,085
Cellulose Fiber + SP 10,338 $72,742
Soil 86,462 $      392
Soil + SP 85,597 $  3,596
Recycled Paper 27,289 $50,256
Recycled Paper + SP 27,016 $50,766

SP: sodium polyacrylate

Future Plans

To confirm the swelling ratios calculated in the lab are realistic, further testing of the effectiveness of the recommended base construction will be needed at field-scale. Additionally, analysis of evapotranspiration, rainfall, and temperature in the piles should be collected to build a working relationship of the leachate rates to important environmental conditions and provide insight into the variable water quantities that change with geographical location. Combining these measurements with climate information will form a better predictive model for broader applicability.

Authors

Presenting author

Alexis Samson, Undergraduate Researcher, Department of Biological Systems Engineering, University of Nebraska-Lincoln

Corresponding author

Amy Schmidt, Professor, Department of Biological Systems Engineering and Department of Animal Science, University of Nebraska-Lincoln, aschmidt@unl.edu

Additional authors

Mara Zelt, Research Technologist, University of Nebraska-Lincoln

Gustavo Castro Garcia, Graduate Research Assistant, University of Nebraska-Lincoln

Additional Information

    1. Ritter, W. F. & Chirnside A. E. M. (1995). Impact of Dead Bird Disposal Pits on Groundwater Quality on the Delmarva Peninsula, Bioresource Technology. https://www.researchgate.net/publication/256637308_Impact_of_dead_bird_disposal_pits_on_ground-water_quality_on_the_Delmarva_Peninsula.
    2. Costa, T. & Akdeniz, N. (2019). A review of the animal disease outbreaks and biosecure animal mortality composting systems, Waste Management. https://www.sciencedirect.com/science/article/pii/S0956053X19302600?via%3Dihub.
    3. Castro, G., Schmidt, A. (2023). Evaluation of Swine Cadaver Disposal through Composting and Shallow Burial with Carbon (poster presentation). ASABE AIM. Omaha, NE.
    4. Code of Federal Regulations, Chapter 40, Part 503. 1993. Standards for the Use or Disposal of Sewage Sludge. Appendix B.   https://www.ecfr.gov/current/title-40/chapter-I/subchapter-O/part-503.
    5. Demitri, C., Scalera, F., Madaghiele, M., Sannino, A., & Maffezzoli, A. (2013). Potential of Cellulose-Based Superabsorbent Hydrogels as Water Reservoir in Agriculture, International Journal of Polymer Science. https://onlinelibrary.wiley.com/doi/10.1155/2013/435073?msockid=06caea3aa704636306b4f95fa67a62b8.

Acknowledgements

This project was partially supported by the National Pork Board Award #22-073. The technical assistance of Maddie Kopplin and Josh Mansfield was critical to the completion of this study.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7–11, 2025. URL of this page. Accessed on: today’s date. 

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Methane leakage imaging, detection, and quantification from dairy manure biogas capture systems

Purpose

One of the key reasons to implement manure anaerobic digestion (AD) to energy or an impermeable cover and flare (CF) system is to reduce greenhouse gas (GHG) emissions, especially methane (CH4), a potent GHG that makes up most of the US agricultural footprint. These systems that process or store manure, commonly liquid dairy or swine manure, are often referred to as biogas capture systems because they keep oxygen out and contain the manure gases that form primarily from the breakdown of organic matter by microorganisms. The biogas captured is then directed through collection pipes to a utilization system, where the goal is to convert the methane to the less potent carbon dioxide (CO2) via either combustion or electrochemical conversion. For AD systems, the biogas collected is consistent enough to burn or convert for useful energy. For CF systems, particularly those used in the Northeast and Upper Midwest, the biogas collected under the liquid manure storage cover is highly variable throughout the day and year, making it more suitable to flare the methane in the biogas rather than harvest energy. Biogas capture systems must be operated and maintained to avoid methane leaks and venting, particularly to realize their carbon reduction value that can often be monetized. Tools to easily identify point-source biogas losses, such as an optical gas imaging (OGI) camera, are still relatively costly for a bioenergy operation, however they can be used to periodically survey and conduct find it and fix it campaigns to repair and correct problems that may have gone unseen to the naked eye. The ability to better understand where and how biogas leaks and vents occur in AD and CF systems enables better design, operation, maintenance, and public confidence.

What Did We Do?

Twelve biogas capture systems operating on commercial dairy farms in NYS were surveyed once per quarter for at least a year for point-source methane losses using an optical gas imaging (OGI) camera (Teledyne FLIR GF77 uncooled) tuned to the infrared spectrum wavelength range (7 – 8.5 micrometers) where methane gas is absorbed. Any methane loss visualized with the OGI camera was recorded and its characteristics described and reported back to the farm or system owner. Other observations about the methane loss were recorded and losses were measured and/or quantified when feasible. The apparent size of the biogas loss was recorded, primarily by distinguishing between OGI visibility in “normal” camera mode versus “high sensitivity mode (HSM)”. Unique losses versus repeated (by visit) were tracked, indicating ease and motivation to correct the loss. Biogas vents were distinguished from biogas leaks, by characterizing a leak as an unknown or unintended biogas loss during normal operation. Biogas venting was considered loss that occurred by design during abnormal operating conditions, such as overpressure in the digester vessel that could not be immediately corrected with flaring excess biogas.

What Have We Learned?

This work is continuing through this year, and eight sites are completed so far. The results from those sites, that include four AD to energy systems (three electricity generation and one biomethane production) and four CF dairy manure storage systems, have generally highlighted that AD systems experience biogas venting more than biogas leaking whereas CF systems experience more leaking than venting. The number of unique biogas losses found was higher in CF systems than in AD systems, which may be due to their much larger biogas capture surface area that is also susceptible to damage from wind, wildlife, and thermal stress. Additionally, the biogas collection and flare struggle with variable biogas flow, quality, and operational robustness that results in lack of combustion during prolonged periods of the year. Another observation, which requires additional data collection from AD to biomethane systems to have confidence in, is that AD to electricity systems can result in biogas venting and/or unnoticed leaking when the biogas produced is greater than what the installed electric capacity can utilize. Additionally, most if not all AD to biomethane systems are instrumented to detect and measure biogas losses as part of their verification requirements for carbon market programs, making it less likely for losses to go unnoticed or unaddressed.

Future Plans

A methane loss detection protocol for both AD to energy systems and CF manure storage systems was developed by Cornell CALS PRO-DAIRY that has been improved during this project and will continue to evolve. Once the full 12 sites are completed, the protocol will be shared more broadly for reference, and best practices recommended for operations and maintenance to prevent, find, and correct biogas losses. Follow on work may include additional methane loss detection with total loss measurement of AD vessels and manure storage covers, to verify assumed loss rates used as defaults in GHG accounting.

Authors

Presenting & corresponding author

Lauren Ray, Sr. Extension Associate, Cornell University – PRO-DAIRY, LER25@cornell.edu

Additional authors

Jason P. Oliver, Dairy Environmental Systems Engineer, Cornell University PRO-DAIRY;

Peter Wright, Agricultural Engineer, Cornell University

Additional Information

https://cals.cornell.edu/pro-dairy/our-expertise/environmental-systems/climate-environment

Acknowledgements

This work is sponsored by the New York State Department of Agriculture and Markets. Special thanks to our collaborating dairy farms and biogas capture system operators.

 

The authors are solely responsible for the content of these proceedings. The technical information does not necessarily reflect the official position of the sponsoring agencies or institutions represented by planning committee members, and inclusion and distribution herein does not constitute an endorsement of views expressed by the same. Printed materials included herein are not refereed publications. Citations should appear as follows. EXAMPLE: Authors. 2025. Title of presentation. Waste to Worth. Boise, ID. April 7-11, 2025. URL of this page. Accessed on: today’s date. 

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Evaluation of the aerosol transmission of the porcine reproductive and respiratory (PRRS) virus from swine production systems

Purpose

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major concern to the U.S. swine industry due to the severe economic loss it can cause. Its symptoms include severe flu-like symptoms, respiratory distress, fever, and premature abortions in pregnant sows. The virus is spread during close contact between pigs or exposure to contaminated urine, semen, feces, and nasal and mammary secretions (1). Control measures have proven exceedingly costly with PRRSV which causes an estimated $1 billion in lost production in the U.S. pork industry per year (3), an 80% increase from a decade earlier (2)(4). With very few, truly effective methods available to control PRRSV after the start of an outbreak, developing methods to mitigate the dispersion of the virus has become a major priority.

Common biosecurity measures for swine operations (e.g., controlled access, personal hygiene, animal management, pest control, and production area cleaning and disinfection) have proved insufficient to stop PRRSV transmission. Producers are, therefore, seeking to understand the potential risks posed by more novel transport methods. Observations of new PRRSV cases emerging during manure handling activities have raised questions about aerosolized manure as a potential transmission vector. This study was conducted to test this possibility in the following stages:

    1. Verify the presence of viable virus sample within pit manure, lagoon samples, or dust coming from barns with active PRRSv outbreaks.
    2. Develop a reliable method for collecting and preserving viable airborne viral samples.
    3. Assess the aerosol transmission “footprint” of PRRSV originating from positive swine farms to improve understanding of potential farm-to-farm disease transmission risks.

What Did We Do?

Novel air sampling devices were constructed by the project team (Figure 1) to be deployed inside and outside swine production units to accumulate samples of particulates and aerosols. The devices accommodate a commercially available Air Prep filter cartridge (innovaprep.com) to capture particulates pulled across the filter by a fan housed within the sampling unit.

Figure 1. Air sampler unit constructed for this project (L) and commercial AirPrep Filter (R)
Figure 1. Air sampler unit constructed for this project (L) and commercial AirPrep Filter (R)

 

 

 

 

Our project team worked closely with the lead veterinarian at a large swine integrator in Nebraska to access farms within 5 to 7 d of pigs being confirmed PRRSV-positive. Sampling events 1 and 2 focused on evaluating PRRSV presence on indoor surfaces, fresh and stored manure, flies, and maggots. Sampling events 3 through 5 focused on evaluating PRRSV presence in air downwind of PRRSV-positive swine production areas or downwind of land application of manure from PRRSV-positive animals.

Sampling Event 1. A swine breeding operation was identified where animals were currently testing positive for and showing clinical signs of PRRSV infection. At this site, two production areas were selected at random for sampling. Surface swabs were collected from floors, fan louvers, and pen dividers. Fresh fecal samples were collected from sows in the same production areas, and an air sampler was placed on the floor in each room and allowed to operate for two hours before retrieving the filters. For surface samples, sterile swabs were swept over each surface type and then placed into phosphate buffered saline (PBS) elution buffer. Fresh fecal samples were collected using a sterile spatula and placed into clean sample containers. Upon retrieving filters from air samplers, a sterilized knife was used to separate the filter from the plastic casing in which it was mounted, and sterile forceps were used to transfer the filter into a PBS elution tube. All samples were transported on ice to the University of Nebraska-Lincoln (UNL) Schmidt Lab and then submitted to the Iowa State University Veterinary Diagnostic Laboratory for analysis by polymerase chain reaction (PCR).

Sampling Event 2. A swine finisher unit was identified where animals were currently testing positive for and showing clinical signs of PRRSV infection. At this site, two production areas were selected at random for sampling inside the building. Surface swabs were collected from floors, fan louvers, feeders, and pen dividers. An air sampler was placed on the floor in each room and allowed to operate for four hours before retrieving the filters. Additional air samplers were mounted outside the building. For one production area, three samplers were mounted at a height aligning with the center of a minimum ventilation fan and spaced at 5, 12, and 19 feet from the rim of the fan hood. For a second production area, two samplers were mounted at a height aligning with the center of a minimum ventilation fan and spaced at 5 and 13 feet from the rim of the fan hood. These samplers were allowed to run for three hours before filters were retrieved. For surface samples, sterile swabs were swept over each surface type and then placed into PBS elution buffer. Manure samples from two deep pit storage sections of the building were collected using a plastic pole and dipper cup and placed into clean plastic bottles. Maggots observed in one pump out port were collected by hand and placed into PBS elution buffer. Upon retrieving filters from air samplers, a sterilized knife was used to separate the filter from the plastic casing in which it was mounted, and sterile forceps were used to transfer the filter into a PBS elution tube. Flies present around the production buildings were also collected at this site. For one sample, approximately six flies were captured and placed directly into PBS elution buffer. For a second sample, approximately six flies were captured, placed into 70% EtOH for 10 s, and then transferred from the ethanol to PBS elution buffer. All samples were transported on ice to the UNL Schmidt Lab and then submitted to the Iowa State University Veterinary Diagnostic Laboratory for analysis by PCR.

Sampling Event 3. A naturally-ventilated PRRSV-positive swine farm was identified. Air samplers mounted on t-posts were deployed in an array at a height above the ground of roughly 6 ft at varying distances (10 yards to 1 mile) from the buildings after using smoke candles to confirm wind direction and dispersion. Sampling was conducted for approximately 2.5 hours on a day with 40-55°F temperature,10-20 mph winds, and full cloud cover (Figure 2).

Sampling Event 4. At a mechanically-ventilated PRRSV-positive swine farm, sampling was conducted using the same process as for Event 3 for approximately 21.25 hours starting on a day with 85-105°F temperature, 4-10 mph winds, and full sun exposure, then continuing overnight.

Sampling Event 5. Using the previously described process, sampling was conducted for approximately 2.5 hours on a day with 70-95°F temperature, 2-10 mph winds, and partly cloudy conditions downwind of a field where lagoon effluent from PRRSV-positive pigs was being applied via center pivot.

Figure 2. Air sampler array at the naturally ventilated swine farm
Figure 2. Air sampler array at the naturally ventilated swine farm

All samples were submitted to the Iowa State Veterinary Diagnostic Lab for RT-qPCR analysis to identify PRRS viral genomic material.

What Have We Learned?

Results of PCR analyses for sampling event 1 (Table 1) revealed that, in barns where swine oral fluid samples were positive for PRRSv, all surface samples collected were also positive or suspected positive for PRRSv. The same was true for all of the surface and air samples collected inside the barn and for the air samples located up to 19 ft minimum from the building ventilation fans during sampling event 2 (Table 2). Maggots taken from the manure pit during sampling event 2, along with sterilized and unsterilized flies, tested positive for PRRSV, as well. Conversely, all manure samples obtained during sampling event 2 tested negative using the methodologies employed. This outcome does not dismiss manure as a possible transmission source; rather, it underscores the need for ongoing research to develop a reliable detection method for PRRS within such a complex matrix.

The team has not yet recovered air samples testing positive for PRRSV from any of the exterior arrays in sampling events 3-5 (Table 3). This could be due to ambient air conditions during the tests which may have caused rapid destruction of the virus or dilution of the virus below detectable concentrations. The rolling terrain surrounding facilities where arrays of samplers were posted downwind of buildings or the land application site may have created turbulent air movement that diluted samples such that concentrations of PRRSV genomic material capture on filters were too low to produce a positive result by PCR.

Table 1. Cycle Threshold (Ct) values for sampling event 1

Sample Description Ct (Result)
Pen Floor, Room 17 37.5 (Suspect)
Fan Louver, Room 17 30.1 (Positive)
Feeder, Room 17 31.6 (Positive)
Air Filter, Room 17 31.2 (Positive)
Pen Floor, Room 18 31.5 (Positive)
Fan Louver, Room 18 31.4 (Positive)
Feeder, Room 18 37.6 (Suspect)
Air Filter, Room 18 30.5 (Positive)
Fecal Sample 1 ³40 (Negative)
Fecal Sample 2 ³40 (Negative)

Cycle threshold (Ct) indicates the number of PCR cycles required for the sample fluorescence to reach a predefined threshold for identification (<38 = positive, ~38-40 = suspect, ≥40 = negative). Lower Ct values correspond to higher viral RNA concentration.

Table 2. Cycle Threshold (Ct) values for sampling event 2

Sample Description Ct (Result)
Exhaust Air, Room 5, 5 ft from fan 33.1 (Positive)
Exhaust Air, Room 5, 12 ft. from fan 34.1 (Positive)
Exhaust Air, Room 5, 19 ft. from fan 38.1 (Suspect)
Indoor Air, Room 5, Rep 1 30.9 (Positive)
Indoor Air Room 5, Rep 2 33.3 (Positive)
Exhaust Air, Room 6, 5 ft from fan 32.6 (Positive)
Exhaust Air, Room 6, 13 ft. from fan 32.4 (Positive)
Flies 37.0 (Suspect)
Flies Sterilized in Ethanol 36.3 (Positive)
Maggots 39.9 (Suspect)
Floor, Room 5, Rep 1 32.4 (Positive)
Floor, Room 5, Rep 2 32.3 (Positive)
Louvers, Room 5, Rep 1 33.1 (Positive)
Louvers, Room 5, Rep 2 32.1 (Positive)
Pens, Room 5, Rep 1 37.9 (Positive)
Pens, Room 5, Rep 2 35.8 (Positive)
Feeder, Room 5, Rep 1 35.8 (Positive)
Feeder, Room 5, Rep 2 37.5 (Suspect)
Pens, Room 4, Rep 1 35.6 (Positive)
Pens, Room 4, Rep 2 35.3 (Positive)
Floor, Room 4, Rep 1 31.4 (Positive)
Floor, Room 4, Rep 2 32.9 (Positive)
Louvers, Room 4, Rep 1 33.0 (Positive)
Louvers, Room 4, Rep 2 32.1 (Positive)

Cycle threshold (Ct) indicates the number of PCR cycles required for the sample fluorescence to reach a predefined threshold for identification (<38 = positive, ~38-40 = suspect, ≥40 = negative). Lower Ct values correspond to higher viral RNA concentration.

Table 3. Cycle Threshold (Ct) values for sampling events 3 through 5

Sampling Event Sample Description Ct (Result)
Event 3 Air Filters (n=2) ³40 (Negative)
Event 4 Air Filters (n=4) ³40 (Negative)
Fans (n=4) ³40 (Negative)
Oral Fluids, Room 15 34.0 (Positive)
Oral Fluids, Room 16 36.1 (Positive)
Oral Fluids, Room 17 38.0 (Suspect)
Oral Fluids, Room 18 34.7 (Positive
Event 5 Air Filters (n=4) ³40 (Negative)

Cycle threshold (Ct) indicates the number of PCR cycles required for the sample fluorescence to reach a predefined threshold for identification (<38 = positive, ~38-40 = suspect, ≥40 = negative). Lower Ct values correspond to higher viral RNA concentration.

Future Plans

It is essential to identify which ambient weather conditions, if any, are favorable for air dispersion of infective PRRSv and which conditions will significantly limit dispersion. As research continues, the suspected ideal conditions for sampling downwind of mechanically ventilated PRRSv-positive barns or irrigation systems applying lagoon effluent from PRRSv-positive pigs will be 0 to 50°F with low to moderate wind speed and full cloud cover. At least 24 hours of continuous sampling is also expected to produce greater opportunity for positive air samples.

The continued inability to isolate the virus from manure samples is curious, given the universally positive samples we identified from the positive barns. However, the PRRSV is believed to require as few as 10 viral particles to be transmitted. Given the potentially very low concentration of viral material in manure, and the significant PCR inhibitors present in complex organic samples, the team continues to explore new sample preparation and testing methods for this matrix.

Lastly, further investigation into the potential roles of flies and maggots is warranted, particularly with the discovery of sufficient PRRSV genomic material in the gut of surface sterilized flies to yield a positive PRRSV result via RT-qPCR.

Authors

Presenting author

Logan Hafer, Undergraduate Research Assistant, Department of Biological Systems Engineering, University of Nebraska-Lincoln

Corresponding author

Dr. Amy Millmier Schmidt, Professor, Department of Biological Systems Engineering and Department of Animal Science, University of Nebraska-Lincoln, aschmidt@unl.edu

Additional author(s)

Dr. Benny Mote, Associate Professor, Department of Animal Science, University of Nebraska-Lincoln

Dr. Hiep Vu, Associate Professor, Department of Animal Science, University of Nebraska-Lincoln

Additional Information

    1. Porcine Reproductive and Respiratory Syndrome virus (PRRSV). Iowa State University – College of Veterinary Medicine; 2024 [accessed 2024 November 22]. https://vetmed.iastate.edu/vdpam/FSVD/swine/index-diseases/porcine-reproductive.
    2. Butler, J. E., Lager, K. M., Golde, W., Faaberg, K. S., Sinkora, M., Loving, C., & Zhang, Y. I. 2014. Porcine reproductive and respiratory syndrome (PRRS): an immune dysregulatory pandemic. Immunologic research, 59, 81-108. https://link.springer.com/article/10.1007/s12026-014-8549-5.
    3. Dee, S., T. Clement, and E. Nelson. 2023. Transmission of porcine reproductive and respiratory syndrome virus in domestic pigs via oral ingestion of feed material. J of the Am Vet Med Assoc, 262(1). https://doi.org/10.2460/javma.23.08.0447
    4. Osemeke, O.H., T. Donovan, K. Dion, D.J. Holtkamp and D.C.L. Linhares. 2021. Characterization of changes in productivity parameters as breeding herds transitioned through the 2021 PRRSV Breeding Herd Classification System. J Swine Health Prod. 2022;30(3):145-148. https://doi.org/10.54846/jshap/1269

Acknowledgements

Funding for this research was provided by the Nebraska Pork Producers Association under award #22-063 and an Undergraduate Student Research Program award from the UNL Institute of Agriculture and Natural Resources, Agricultural Research Division.

 

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